Interfering near field transducer for energy assisted magnetic recording

ABSTRACT

An apparatus for energy assisted magnetic recording of a storage disk includes a plurality of dielectric waveguide cores configured to receive incident light energy from an energy source and direct the incident light energy to a target, and a near field transducer (NFT) formed at an air bearing surface of a magnetic recording device. The NFT is configured to focus the light energy received from the plurality of waveguide cores and to transmit the focused light energy onto the storage disk surface to generate a heating spot on the storage disk. The NFT includes a plurality of propagating surface plasmon polariton (PSPP) elements configured as plasmonic metal ridges. Each of the PSPP elements has a width approximately equivalent to the width of the heating spot and is disposed above a surface of a single waveguide core in a longitudinal alignment.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No. 14/324,466, filed on Jul. 7, 2014, which claims the benefit of U.S. Provisional Application Ser. No. 62/010,038 filed on Jun. 10, 2014, both of which are expressly incorporated by reference herein in their entirety.

BACKGROUND

High density storage disks are configured with layers of materials that provide the required data stability for storage. The magnetic properties of the media require a softening when writing to the disk to change the bit state. Energy Assisted Magnetic Recording (EAMR) device or Heat Assisted Magnetic Recording (HAMR) technology provides heat that is focused on a nano-sized bit region when writing onto a magnetic storage disk, which achieves the magnetic softening. A light waveguide directs light from a laser diode to a near field transducer (NFT). The NFT focuses the optical energy to a small spot on the target recording area which heats the magnetic storage disk during a write operation. Inefficiencies in the NFT can have a negative impact on the power budget of the laser diode and the EAMR/HAMR system lifetime. Higher NFT efficiency allows for lower laser power demand, relieving EAMR/HAMR system requirement on the total optical power from the laser source, and results in less power for parasitic heating of the EAMR/HAMR head resulting for improved reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of the present invention will now be presented in the detailed description by way of example, and not by way of limitation, with reference to the accompanying drawings, wherein:

FIG. 1 shows a diagram of an exemplary hard disk drive;

FIG. 2 shows a diagram of an exemplary embodiment of a near field transducer formed with two propagating surface plasmon polariton elements;

FIG. 3 shows a diagram of an exemplary embodiment of a near field transducer with two propagating surface plasmon polariton elements and a plasmonic metal cap.

FIG. 4 shows a diagram of an exemplary embodiment of a near field transducer formed with three propagating surface plasmon polariton elements; and

FIG. 5 shows a diagram of an exemplary embodiment of a near field transducer formed with a plurality of propagating surface plasmon polariton elements that is not equal in number to a plurality of corresponding waveguide cores.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appended drawings is intended as a description of various exemplary embodiments and is not intended to represent the only embodiments that may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of the embodiments. However, it will be apparent to those skilled in the art that the embodiments may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form in order to avoid obscuring the concepts of the embodiments. Acronyms and other descriptive terminology may be used merely for convenience and clarity and are not intended to limit the scope of the embodiments.

The various exemplary embodiments illustrated in the drawings may not be drawn to scale. Rather, the dimensions of the various features may be expanded or reduced for clarity. In addition, some of the drawings may be simplified for clarity. Thus, the drawings may not depict all of the components of a given apparatus.

Various embodiments will be described herein with reference to drawings that are schematic illustrations of idealized configurations. As such, variations from the shapes of the illustrations as a result of manufacturing techniques and/or tolerances, for example, are to be expected. Thus, the various embodiments presented throughout this disclosure should not be construed as limited to the particular shapes of elements illustrated and described herein but are to include deviations in shapes that result, for example, from manufacturing. By way of example, an element illustrated or described as having rounded or curved features at its edges may instead have straight edges. Thus, the elements illustrated in the drawings are schematic in nature and their shapes are not intended to illustrate the precise shape of an element and are not intended to limit the scope of the described embodiments.

The word “exemplary” is used herein to mean serving as an example, instance, or illustration. Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments Likewise, the term “embodiment” of an apparatus or method does not require that all embodiments include the described components, structure, features, functionality, processes, advantages, benefits, or modes of operation.

As used herein, the term “about” followed by a numeric value means within engineering tolerance of the provided value.

In the following detailed description, various aspects of the present invention will be presented in the context of an interface between a waveguide and a near field transducer used for heat assisted magnetic recording on a magnetic storage disk.

FIG. 1 shows a hard disk drive 111 including a disk drive base 114, at least one rotatable storage disk 113 (e.g., such as a magnetic disk, magneto-optical disk), and a spindle motor 116 attached to the base 114 for rotating the disk 113. The spindle motor 116 typically includes a rotating hub on which one or more disks 113 may be mounted and clamped, a magnet attached to the hub, and a stator. At least one suspension arm 108 supports at least one head gimbal assembly (HGA) 112 that holds a slider with a magnetic head assembly of writer and reader heads. A ramp assembly 100 is affixed to the base 114, and provides a surface for tip of the suspension arm 108 to rest when the HGA 112 is parked (i.e., when the writer and reader heads are idle). During a recording operation of the disk drive 111, the suspension arm 108 rotates at the pivot 117, disengaging from the ramp assembly 100, and moves the position of the HGA 112 to a desired information track on the rotating storage disk 113. During recording, the slider is suspended by the HGA 112 with an air bearing surface of the slider that faces the rotating disk 113, allowing the writer head to magnetically alter the state of the storage bit. For heat assisted magnetic recording, a near field transducer (NFT) on the air bearing surface may couple light energy from a waveguide to produce a heating spot on the rotating disk 113 for magnetically softening the bit space.

FIG. 2 shows a diagram of an exemplary embodiment of an NFT 200 arranged at an air bearing surface (ABS) 210 of a slider which carries a magnetic head assembly. The ABS 210 is the surface of the slider facing the storage disk 113. As the slider flies over the storage disk 113, a cushion of air is maintained between the slider and the disk 113. As shown, two dielectric waveguide (WG) cores 211, 212 are arranged to each carry light energy into the NFT 200 directed toward a common target. The light energy may be generated by a common laser diode source (not shown) that may be split in half by a splitter (not shown). The dielectric waveguide cores 211, 212 may be of equal length to ensure that the combined energy wave at the ABS 210 is in substantial phase alignment for constructive interference and maximum energy emission to the storage disk 113. Alternatively, dielectric waveguide cores 211, 212 may be of unequal length such that the incident energy waves may have a particular phase difference that optimizes constructive interference and maximum energy magnitude at the ABS 210. The two waveguide cores 211, 212 are substantially linear and converge at a junction near the ABS 210 at an interior angle between 0 and 180 degrees, (e.g., approximately 90 degrees as shown in FIG. 2). The dielectric material of the waveguide core 211, 212 may be Ta₂O₅ for example.

As shown in FIG. 2, a plasmonic metal ridge element 201, 202 may be disposed above each waveguide core 211, 212 in a longitudinal direction along the center the waveguide core surface. The optical energy from the dielectric waveguide core 211, 212 in proximity with of the plasmonic metal ridge 201, 202 energizes propagating surface plasmon polaritons (PSPPs) along a surface of the plasmonic metal ridge 201, 202 toward the ABS 210. Thus, each plasmonic metal ridge element 201, 202 may function as a PSPP element. The material of the plasmonic metal ridge element 201, 202 may be a gold alloy, for example. Other examples of plasmonic metals that may be used to form the metal ridge element 201, 202 include silver or copper alloys. As shown in the cross section, a gap (e.g., about 20 nm) may exist between the plasmonic metal ridge element 201, 202 and the dielectric waveguide core 211, 212. Alternatively, the gap may be omitted, and the plasmonic metal ridge element 201, 202 may directly contact the dielectric waveguide core 211, 212, at least for a portion of the plasmonic metal ridge element 201, 202. The two dielectric waveguide cores 211, 212 and the entire NFT 200, including the two plasmonic metal ridges 201, 202, may be encapsulated by a silicon oxide material. The plasmonic metal ridge elements 201, 202 may thus be suspended above the dielectric waveguide cores 211, 212 within the waveguide cladding and/or slider substrate material.

The plasmonic metal ridge elements 201, 202 may be configured as shown in FIG. 2, converging at a junction above the junction of the dielectric waveguide cores 211, 212. The junction of plasmonic metal ridge elements 201, 202 may occur on a common plane, or may be formed by overlapping one element over the other element. As shown, a single metal ridge extension 203 may be formed and configured to be perpendicular with the ABS 210, extending from the junction of plasmonic metal ridge elements 201, 202. This extension 203 may provide a focal point for the NFT 200 energy output at the ABS 210 for heating the target bit space for recording data. For example, the endpoint of the extension 203 may function as an emitter for the NFT 200 energy output. Alternatively, the extension 203 may be omitted, and the junction of plasmonic metal ridge elements 201, 202 may be formed at the ABS 210. For example, an NFT energy output emitter may be formed at the ABS 210 by the exposed metal ridge junction at the ABS 210, from which the maximum energy is propagated across the air cushion and onto the surface of storage disk 113. The physical dimension of the emitter (i.e., the width of the exposed junction of plasmonic metal ridge elements 201, 202 or extension 203) may be approximately equivalent to the size of the focused heating spot on the surface of the disk 113. The target size of the heating spot is dependent on the track size as the slider flies over the track, which may be about 10-70 nm wide for example. The size of the heating spot also depends on the distance between the ABS 210 and the disk 113. The focus of the heating spot may be optimized by minimizing the gap. The width of the plasmonic metal ridge element 201, 202 may also be significantly smaller than the width of the dielectric waveguide core (e.g., 300-500 nm). Also, the height of the metal ridge element 201, 202 may be about 10-70 nm for example.

The two PSPP element configuration as shown in FIG. 2 may provide approximately twice as much electrical field magnitude compared with a configuration of a single PSPP element arranged perpendicular to the ABS 210, driven by a common total input power in the waveguide system. The constructive interference produced by the two PSPP elements 201, 202 allows improved efficiency of energy delivery from the laser diode source, which translates to longer service life of the EAMR/HAMR device. To optimize the efficiency of the two PSPP element configuration, each PSPP element 201, 202 is configured with a length L which is an integer multiple of coupling length Lc from dielectric waveguide core to the PSPP element 201, 202 (e.g., for Lc of 1200 nm, the length of the PSPP element should be about a(1200 nm) where a is an integer value). With the PSPP element 201, 202 having a length L approximately equivalent to aLc ensures that the maximum energy transfer propagates from the PSPP element 201, 202 at the ABS 210. If the length of the PSPP element 201, 202 deviates from aLc, some of the energy wave may be lost to the dielectric waveguide core 211, 212.

The NFT 200 does not have to be limited to two interfering PSPP elements 201, 202 as shown in FIG. 2. In an alternative embodiment, N (a positive integer) PSPP elements interfere at the ABS, which may provide approximately N times increase of the electrical field magnitude, driven by a common total input power in the waveguide system. The value of N can increase beyond 2 or 3, until other parasitic interferences within the three dimensional layout the EAMR head becomes a limiting factor. For N≧3, the PSPP elements may be arranged in a three dimensional configuration.

FIG. 3 shows an alternative exemplary arrangement for an NFT 300, which is a variation of NFT 200 with an additional plasmonic metal cap 305. As shown in FIG. 3, the NFT 300 may include the plasmonic metal ridge elements 202, 203 coupled to a plasmonic metal cap 305 above. For illustrative purpose, the plasmonic metal element 305 is depicted as transparent to reveal the fine ridge features 201, 202 below. The plasmonic metal cap 305 is shown in a semi-circle configuration with a straight edge substantially aligned with the ABS 210. The aligned edge of the plasmonic metal cap 305 may be recessed from the ABS 210. The material of the plasmonic metal ridge elements 201, 202 and the plasmonic metal cap 305 may be a gold alloy, for example. Other examples of plasmonic metals that may be used to form the metal ridge elements 201, 202 and plasmonic metal cap include silver or copper alloys. The two dielectric waveguide cores 211, 212 and the entire NFT 200, including the plasmonic metal cap 305 and two plasmonic metal ridges 201, 202, may be encapsulated by a silicon oxide material.

The thickness of the plasmonic metal cap 305 is not a significant factor in achieving the precise nano-sized heating spot, and therefore the thickness may be configured according to providing adequate heat transfer for controlling the peak temperature in the NFT 300. The plasmonic metal element 305 configuration is determined by a shape and size necessary to be coupled with the metal ridge features 201, 202 (i.e., a footprint that covers the metal ridge features 201, 202). As an example, the size of a semi-circle shaped plasmonic metal element 305 may be 1000 nm in diameter and greater than 100 nm in thickness. The surface of the plasmonic metal cap 305 may be configured to have a substantially flat surface facing the metal ridge features for coupling, while the opposite surface may be flat, rounded or irregular such that the overall thickness is variable. While shown in FIG. 3 as a semi-circle shape, the plasmonic metal cap 305 may be configured in shapes other than a semi-circle, such as a rectangular or polygonal block.

The NFT 300 does not have to be limited to two interfering PSPP elements 201, 202 as shown in FIG. 3. In an alternative embodiment, N (a positive integer) PSPP elements interfere at the ABS, which may provide approximately N times increase of the electrical field magnitude. The value of N can increase beyond 2 or 3, until other parasitic interferences within the three dimensional layout the EAMR head becomes a limiting factor. For N≧3, the PSPP elements may be arranged in a three dimensional configuration. The plasmonic metal cap 305 would also conform to a corresponding three dimensional configuration as being coupled to the N PSPP elements from above.

FIG. 4 shows an alternative exemplary arrangement for an NFT 400 having N=3 PSPP elements. Each PSPP element is formed in a manner similar to that described above for the two-PSPP element configuration shown in FIG. 4 and described above. The NFT 400 may include a plasmonic metal cap 405 and plasmonic metallic ridge elements 401, 402, 403 arranged above each respective dielectric waveguide core 411, 412, 413 as shown in FIG. 4. For illustrative purpose, the plasmonic metal element 405 is depicted as transparent to reveal the fine ridge features 401, 402, 403 below. A gap may exist between each plasmonic metal ridge element 401, 402, 403 and the respective dielectric waveguide core 411, 412, 413. The three dielectric waveguide cores 411, 412, 413 and the entire NFT 400, including the plasmonic metal cap 405 and three plasmonic metal ridge elements 401, 402, 403, may be encapsulated by silicone oxide material. The plasmonic metal ridge elements 401, 402, 403 may be configured as shown in FIG. 4, converging at a junction above the junction of the dielectric waveguide cores 411, 412, 413. The junction of plasmonic metal ridge elements 401, 402, 403 may occur on a common plane, or may be formed by overlapping one element over the other elements. As shown, a single metal ridge extension 423 may be formed and configured to be perpendicular with the ABS 410, extending from the junction of plasmonic metal ridge elements 401, 402, 403. This extension 423 may provide a focal point for the NFT energy output at the ABS 410 for heating the target bit space for recording data. Alternatively, the extension 423 may be omitted, and the junction of the three plasmonic metal ridge elements 401, 402, 403 may be formed at the ABS 410. For example, an NFT energy output emitter may be formed at the ABS 410 by the exposed plasmonic metal ridge junction at the ABS 410, from which the maximum energy is propagated across the air cushion and onto the surface of the storage disk 113. The physical dimension of the emitter (i.e., the width of the exposed plasmonic metal ridge junction or extension) may be approximately equivalent to the size of the focused heating spot on the surface of the disk 113. This embodiment of NFT 400 may alternatively be configured without plasmonic metal cap 405.

The number of PSPP elements may vary with respect to the number of dielectric waveguide cores. FIG. 5 illustrates an example where two PSPP elements 501A, 501B may be disposed side-by-side above a single dielectric waveguide core 511. Similarly, PSPP elements 502A, 502B may be disposed side-by-side above a single dielectric waveguide core 512. In this example, NFT power delivery efficiency is increased by five interfering PSPP elements 501A, 501B, 502A, 502B, 503 while using only three dielectric waveguide cores 511, 12, 513. As shown in FIG. 5, the NFT 500 may include the plasmonic metal cap 505 disposed above the PSPP elements 501A, 501B, 502A, 502B and 503. This embodiment of NFT 500 may alternatively be configured without plasmonic metal cap 505.

The various aspects of this disclosure are provided to enable one of ordinary skill in the art to practice the present invention. Various modifications to exemplary embodiments presented throughout this disclosure will be readily apparent to those skilled in the art, and the concepts disclosed herein may be extended to other devices. Thus, the claims are not intended to be limited to the various aspects of this disclosure, but are to be accorded the full scope consistent with the language of the claims. All structural and functional equivalents to the various components of the exemplary embodiments described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. §112(f) unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.” 

What is claimed is:
 1. An apparatus for energy assisted magnetic recording of a storage disk, comprising: at least one dielectric waveguide core configured to receive incident light energy from an energy source and direct the incident light energy to a target; and a near field transducer formed at or near an air bearing surface of a magnetic recording device and configured to focus the light energy received from the at least one dielectric waveguide core and to transmit the focused light energy onto the storage disk surface to generate a heating spot on the storage disk, the near field transducer comprising: at least one propagating surface plasmon polariton (PSPP) configured as a plasmonic metal ridge; wherein the at least one PSPP element is disposed above a surface of the at least one dielectric waveguide core in a longitudinal alignment; and wherein the at least one PSPP element is configured with a width approximately equivalent to the width of the heating spot.
 2. The apparatus of claim 1, further comprising: plasmonic metal cap disposed above the at least one PSPP element and coupled to the at least one PSPP element.
 3. The apparatus of claim 2, wherein the plasmonic metal cap is configured with a straight edge aligned with the air bearing surface.
 4. The apparatus of claim 2, wherein the plasmonic cap is configured with a thickness sufficient for a heat sink to control peak temperature of the near field transducer.
 5. The apparatus of claim 2, wherein the plasmonic cap is configured with a variable thickness.
 6. The apparatus of claim 2, wherein the plasmonic cap is configured with a flat surface for coupling to the at least one PSPP element.
 7. The apparatus of claim 1, wherein a gap exists between the at least one PSPP element and the corresponding surface of the at least one waveguide core.
 8. The apparatus of claim 1, further comprising: at least two dielectric waveguide cores, and at least two PSPP elements, wherein each of the PSPP elements comprises a first end and a second end, wherein the first ends of all PSPP elements are connected together at a junction point near the air bearing surface with at least a portion of the junction exposed on the air bearing surface.
 9. The apparatus of claim 8, further comprising a PSPP element extension configured to be perpendicular with the air bearing surface extending from the junction of PSPP elements.
 10. The apparatus of claim 1, wherein more than one PSPP element is disposed along the at least one waveguide core.
 11. The apparatus of claim 1, further comprising at least three waveguide cores, wherein the at least three waveguide cores and corresponding PSPP elements are configured in three dimensional arrangement with respect to the air bearing surface.
 12. The apparatus of claim 8, wherein the at least two PSPP elements provide constructive interference of the incident light energy at the target.
 13. A magnetic storage disk drive, comprising: a rotatable magnetic storage disk; a laser diode; at least one dielectric waveguide core configured to receive incident light energy from an energy source and direct the incident light energy to a target; and a near field transducer formed at or near an air bearing surface of a magnetic recording device and configured to focus the light energy received from the at least one dielectric waveguide core and to transmit the focused light energy onto the storage disk surface to generate a heating spot on the storage disk, the near field transducer comprising: at least one propagating surface plasmon polariton (PSPP) element configured as a plasmonic metal ridge; wherein the at least one PSPP element is disposed above a surface of a corresponding one of the at least one dielectric waveguide core in a longitudinal alignment; and wherein the at least one PSPP element is configured with a width approximately equivalent to the width of the heating spot. 